1. Field of the Invention
This invention relates to a process for performing the chlorosulfonation of polyethylene by chlorine and sulfuryl chloride or by sulfuryl chloride alone using a specific solvent.
2. Description of the Prior Art
It is known that an elastomer having excellent properties such as weather resistance, heat resistance, etc., is obtained by vulcanizing chlorosulfonated polyethylene having a chlorine content of 25-45% and a sulfur content of 0.3-4%.
The most important point in the case of producing chlorosulfonated polyethylene by dissolving polyethylene in a solvent and reacting the polyethylene with chlorine and sulfuryl chloride or sulfuryl chloride alone is how to uniformly distribute chlorine and a chlorosulfon group on polyethylene and the properties of chlorosulfonated polyethylene greatly change by the distributions of them.
Also, the chlorosulfonation of polyethylene is in the point of destroying the crystal of polyethylene and changing it into an amorphous substance and in this case, a sufficiently high temperature is necessary for fusing the crystals of polyethylene and it is said to be necessary to dissolve polyethylene at a temperature as high as possible and chlorosulfonate polyethylene at a high temperature.
However, in the case of using a low boiling point solvent such as carbon tetrachloride (boiling point 76.7.degree. C.), which is generally used, it is very difficult to perform the uniform distribution of chlorine (U.S. Pat. No. 4,145,491) and even when a chlorination is performed to a considerable extent, the crystals of polyethylene remain in chlorosulfonated polyethylene formed.
Therefore, there is proposed a process of restraining the influence of the crystals of polyethylene as low as possible by performing the production of chlorosulfonated polyethylene in two steps, that is, by performing chlorination of polyethylene with chlorine at a temperature as high as possible (.about.160.degree. C.) in the first step to chlorinate to some extent and chlorosulfonating the polyethylene with sulfuryl chloride in the second step (see, U.S. Pat. No. 2,972,604). However, even in such a process, it is very difficult to establish the condition for obtaining a constant quality in the reaction using a low boiling temperature, such as carbon tetrachloride.
For overcoming the difficulty, a process may be considered wherein using a solvent having a high boiling point and a high dissolving power for polyethylene or the partially chlorinated product of it, polyethylene or the partially chlorinated product thereof is reacted in the solvent at a high temperature, but when such a high-boiling solvent is used, it is difficult to separate and recover the solvent from the polymer solution formed with a good efficiency as well as there are problems on the properties of the product. For example, when a drum drying method is employed for isolating chlorosulfonated polyethylene from the reaction mixture, the polymer formed must be isolated at temperature higher than the boiling point of the solvent used for the reaction and in this case, chlorosulfonated polyethylene is liable to color or deteriorate and also the solvent remains in the polymer to give various undesirable influences on the properties of the elastomer.
Accordingly, there is still a need for a process of producing a high quality chlorosulfonated polyethylene having an excellent quality of an elastomer while obtaining a constant quality product where the chlorine and chlorosulfone groups are uniformly distributed.